Radio system

ABSTRACT

A radio system, including a fixed radio network having base stations and mobile radio stations. Each mobile station with no ongoing call normally monitors messages transmitted by a base station on a control channel in order to enable a fast call set-up. The user may select for a mobile station a normal operating mode, in which messages on the control channel are monitored continuously, as well as an alternative operating mode, in which the mobile station may stop monitoring the control channel at suitable moments for a time of absence known by the radio network, during which time the radio network does not try to send messages to the mobile station.

BACKGROUND OF THE INVENTION

The invention relates to a radio system, comprising a fixed radionetwork having base stations and mobile radio stations, each mobilestation with no ongoing call normally monitoring messages transmitted bya base station on a control channel in order to enable a fast callset-up.

Subscriber units used in mobile telephone systems are oftenhand-portable battery-powered telephones. Because the intention is tomake portable subscriber units as small-sized and light as possible,very contradictory demands are made on the batteries to be used in them,viz. small size and as long operation time as possible by one charge. Toachieve these properties, a portable subscriber unit is usuallyimplemented by means of a technology consuming as little energy aspossible, and the purpose is to minimize unnecessary power consumptionin different ways. It is difficult to reduce the power consumptionduring a call. Also in an idle state, a subscriber unit without anongoing call monitors the control channel of its base station forpossible incoming messages, which implies that at least a receiver, acorresponding synthesizer circuitry as well as a control logic are inoperation. It is not directly possible to entirely switch off thesubscriber unit between calls, because possible messages from the fixednetwork may then be lost. For this reason, some cellular radio networks,such as NMT900 and GSM, use continuously a specific sleeping facilityfor energy saving, by means of which facility the system informs thesubscriber unit by signalling on a control channel how long it may"sleep" safely, i.e. be in a state consuming little energy (with thereceiver and the synthesizer switched off, for instance), without losingmessages. The subscriber unit contains a timer function, which "awakens"the subscriber unit after a predetermined time. The system again attendsto that the messages which have come to the subscriber unit during"sleeping" are not transmitted until the subscriber unit is "awake".However, the sleeping facility as per described above is problematic, ifa fast call set-up time is required in the system simultaneously. Suchsystems are, e.g., private trunking radio networks used for transmittingcommands, etc., from one subscriber to another. A call may come at anymoment, and therefore, the subscriber unit has to be always "awake", sothat a command may be passed through immediately. The wake-up facilityas described above, in which the system controls the subscriber unit "tosleep", might delay a call set-up even by tens of seconds, which is notalways acceptable for all users. For this reason, such a sleepingfacility has not been applied to systems requiring fast call set-up,even though a reduction of power consumption of hand-portable subscriberunits would be very desirable also in these systems.

U.S. Pat. No. 5,150,361 discloses a TDMA or TDMA/FDMA device having twooperating modes: energy saving mode and normal operating mode. In thesystem described in the prior art document, time frames are transmitted,each of them comprising at least two control time slots. In the energysaving mode, all main parts of the device are shut down during theentire frame, except for one control time slot. In the normal operatingmode, the device monitors both control time slots of each frame. In theexample presented in the document, the length of a frame is 180 msec anda frame contains four time slots of 45 msec each. So the device is shutdown for 135 msec in each frame and active for 45 msec. The shut downperiods are thus very short and depend on the length of the time slot,which means only minor savings in energy.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a radio system, whichmay implement a fast call set-up as well as a significant reduction inpower consumption of a subscriber unit by causing the subscriber unit to"sleep" intermittently.

According to one aspect of the invention, the radio system described inthe preamble is characterized in that the user may select for a mobilestation a normal operating mode, in which messages on the controlchannel are monitored continuously, as well as an alternative operatingmode, in which the mobile station may stop monitoring the controlchannel at suitable moments and send an absence message to the radionetwork each time when leaving the control channel, that absence messageinforming of the leaving and the time of absence, during which the radionetwork does not try to send messages to the mobile station.

According to another aspect of the invention, the radio system describedin the preamble is characterized in that the user may select for amobile station a normal operating mode, in which messages on the controlchannel are monitored continuously, as well as an alternative operatingmode, upon selection of which the mobile station (MS) informs the radionetwork and in which the mobile station may stop monitoring the controlchannel at suitable moments during the absence periods known by theradio network, the starting moments of which periods are determined bythe radio network and during which periods the radio network does nottry to send messages to the mobile station.

In order to make two important and mutually contradictory properties,i.e. fast call set-up and sleeping facility, compatible in the radiosystem according to the invention, it is taken into account that theuser of a mobile station can select a normal operating mode providingthe fast call set-up, and a power saving mode, in which parts of thesubscriber unit consuming much energy may be switched offintermittently. The user is able to select the operating mode suitablefor his or her subscriber unit at each moment depending on whether he orshe desires the fastest possible call set-up or to save the batteries ofthe device.

In one embodiment of the invention, a subscriber unit in the powersaving mode sends a message to the radio network each time when leavingthe control channel. The message informs of the leaving and the time ofabsence. Upon receiving such a message, the radio network interrupts thesending of messages to the subscriber unit for the sleeping timeindicated in the message. The messages possibly arriving during thistime are stored and transmitted to the subscriber unit after it hasawakened.

In another embodiment of the invention, a mobile station informs theradio network of the new operating mode immediately when the user haschanged the operating mode. The radio network controls the moments atwhich the subscriber unit in the power saving mode leaves the controlchannel and determines the time of absence.

Alternatively, the subscriber unit may use the time during which it isabsent from the control channel and thus unreachable for the system alsofor something else than battery saving. For instance, the subscriberunit may make measurements on adjacent control channels/base stations inorder to search for the best base station and have it ready, if it isnecessary to change the control channel as a consequence of roaming. Thesubscriber unit may also use the time of absence for establishing aradio connection with another radio system or for a direct radiocommunication with another subscriber unit without a radio system.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described by means of embodimentswith reference to the attached drawings, in which:

FIG. 1 illustrates a radio system, to which the invention may beapplied, and

FIG. 2 is a general block diagram of a mobile radio station.

DETAILED DESCRIPTION

FIG. 1 shows a trunking-type radio telephone system, in which thegeographical area covered by the system is divided into smaller radioareas, i.e. radio cells, C1, C2 and C3, being apart from each other,abutting on each other or overlapping each other at edge areas. Eachcell C1, C2, C3 comprises at least one fixed, typically multichanneltransceiver equipment BS, called a base station. All base stations BSare connected via fixed links, such as cables, to an exchange MX, whichcontrols the operation of the base stations BS. The base stations BS arein radio communication with subscriber radio stations MS moving freelywithin the area of the system, at radio frequencies, i.e. on radiochannels, allocated for the system.

In a trunking-type radio system, several user groups, even several userorganisations, share a common group of channels. The trunking radiotelephone system may be a digital TDMA system or an analog FDMA system.The structure of the analog FDMA system may be of the type described inFinnish Patent Application 914654, for instance. In the analog FDMAsystem, each radio channel constitutes one traffic channel or controlchannel. The term control channel refers generally to a channel orchannels on which is or are transferred control signalling of the systembetween a base station BS and mobile stations MS. The term trafficchannel refers generally to a channel for transferring speech or data.In the TDMA system, each radio channel is further divided into timeslots (e.g. 4 or 8 time slots per one radio channel), in which thecontrol and traffic channels are conveyed.

Call set-up in such a radio system may be of a message-trunking type,with a traffic channel allocated permanently for one call for the wholeduration of the call, or of a transmission-trunking type with a numberof simultaneous calls sharing a particular group of traffic channels insuch a way that a traffic channel from this group is allocatedseparately for each call transaction (for each activation of tangent).The present invention is suitable for being used in connection witheither way of setting up a call.

FIG. 2 shows a general block diagram of a mobile radio station MS. Theblock diagram includes ten functional parts: a control logic 25(microprocessor), a transmitter 23, a receiver 22, a filter unit 21, asynthesizer 24, an audio part 26, an operating unit 27, a timer 28 and apower source 29. The processor unit attends to all control operations ofthe radio unit, keyboard and display operations, signal processing,serial traffic and, possibly, generation of ringing tones and DTMFpostselections. The audio part 26 processes a low-frequency signal fromthe receiver 22 and applies it to a loudspeaker or a handset. The audiopart also processes an outgoing signal from a microphone and provides itwith a correct deviation level before the signal is inputted to anoscillator TXVCO of the synthesizer 24. The synthesizer 24 generates aninjection signal for the receiver 22 and a modulated transmission signalfor the transmitter 23. The synthesizer comprises three parts, viz. thecontrol logic of the synthesizer and the voltage controlled oscillatorsRXVCO and TXVCO for the receiver and the transmitter. The function ofthe receiver 22 is to discriminate and amplify a desired frequency froma signal coming from an antenna ANT and to detect the low-frequencysignal. The receiver 22 outputs the low-frequency signal to the audiopart 26 and the received signalling messages to the processor unit 25.The function of the transmitter 23 is to amplify the modulated signalfrom the TXVCO of the synthesizer 24 to a desired transmission power (ofa few watts). The oscillator TXVCO of the synthesizer 24 modulates alsothe signalling messages inputted by the processor unit, which messagesare then amplified in the transmitter 23. The filter unit 21 separatesthe transmitter and receiver frequencies from each other. In addition,the filter unit comprises a transmission switch S1 (tangent), by whichthe user may manually switch the antenna ANT either to the transmitter23 or the receiver 22. The operating unit 27 constitutes a userinterface between person and machine. The operating unit comprises atleast a keyboard and preferably also a numeric or an alphanumericdisplay. The operating unit may also contain a handset and a microphone.

All above-mentioned parts of the mobile station MS, except the antennaANT and possibly the filter part 21, are active components and consumeelectrical power. Operating voltages V_(cc1) to V_(cc6) for differentblocks are generated by the power source 29. The power source 29 iscontrolled by the processor unit 25 and the timer 28 in a mannerdescribed below.

The user of the MS may select from the operating unit 27, for instancefrom the keyboard, at least two different operating modes for the MS,viz. a normal operating mode and at least one alternative operatingmode, such as power-saving mode (sleeping mode).

An MS in the normal operating mode, with no call going on, monitorscontinuously the control channel of a base station (the base station towhich the MS is currently registered) and waits for a possible incomingmessage. Then at least the receiver 22 and the corresponding parts ofthe synthesizer 24 as well as the audio part 26 and the processor unit25 are in operation (switched on). The transmitter 23 and possibly alsothe operating unit 27 are in sleeping state (switched off). The displayof the operating unit 27 may be in operation also in the sleeping state.

After the user of the MS has activated the power-saving mode, theprocessor unit 25 may control the operation of the MS between thecontrol channel-monitoring mode described above and the sleeping mode,consuming very little energy. When the processor unit 25 desires tocause the MS to sleep, it sends information as to the length of thesleeping period to the sleeping timer 28 (and starts the timer at thesame time) and commands the power source 29 to switch off the operatingvoltages of all other circuits, preferably also those of its own. Afterthe determined sleeping period has expired, the sleeping timer 28 causesthe power source 29 to switch on the operating voltage V_(cc4) of theprocessor unit 25, which then commands the power source 29 to switch onthe operating voltages of the other necessary circuits. The user mayrestore the MS from the sleeping mode any time by pressing any key onthe operating unit, as a consequence of which the power source 29switches on the operating voltage V_(cc4) of the processor unit 25,which then causes the operating voltages of the other necessary circuitsto be switched on. In the second embodiment of the invention, theprocessor unit 25 commands the power source 29 to switch off theoperating voltages of the other units and employs a lower clockfrequency, due to which the power consumption of the processor unit isminimized. As a result, the separate timer 28 may be replaced by a timerinside the processor unit, e.g. by means of software. The processor unitemploys the higher clock frequency again after the sleeping period hasexpired and causes the operating voltages of the other necessarycircuits to be switched on.

Because a sleeping MS is not capable of monitoring the control channelof its base station and thus not capable of observing possibly incomingmessages, the radio network shall be aware of when and for what time theMS is absent from the control channel.

With the MS in the normal operating mode, in which it continuouslymonitors the control channel, the call set-up time is typically of theorder of 0.5 seconds. If the user does not find fast call set-up time asimportant as battery saving, the user selects the power saving mode bymeans of the operating unit, and subsequently, the MS sends to the fixedradio network a message informing that the MS is in the power-savingmode. After this the sleeping periods of the MS will be started from thesystem by means of a specific starting message. Upon receiving such astarting message and noticing that the message concerns the MS itself,the MS enters the sleeping mode described above for a predeterminedtime. This predetermined time is preset in the timer 28 and in the dataof the radio network. The sleeping time may be selected by the operator,and is at least one second, preferably at least 10 to 20 seconds. Anextension of this time prolongs the charging interval of the battery,but also the call set-up time, on the other hand. A suitable time issome compromise between these. The radio network does not send messagesto a sleeping mobile station MS during a sleeping period, but storesthem and does not transmit them until the MS is awake. A radio networkcomponent, typically the exchange MX, controlling the call set-up andtransmitting messages, comprises a data file, into which the systemregisters the mobile stations being in the power-saving mode andrequiring messages to be sent for starting the sleeping mode. The samedata file also includes a real-time information of whether the MS isasleep or awake, in order that the MX will be able not to send messagesduring the sleeping period. This last information is not needed in analternative solution, in which the radio network sends a messageimmediately upon arrival to the MS and repeats the message after thesleeping period has expired, if the MS has not responded. However, ifeach MS is caused to sleep from the radio network, it leads easily to anexcessive load on the control channel. Therefore it is preferable thatthe MSs are caused to sleep in groups, one message controlling aplurality of MSs. The division into groups may be based for instance onthe last digit (or the last bit or the last two bits) in the pagingnumber, which will be included in sleeping messages.

In the second embodiment of the invention, in which the user hasselected the power saving mode, an MX sends an absence message to theradio network each time it leaves the control channel (when being causedto sleep), which message informs of the leaving and the time of absence.Then the radio network stops sending messages to the mobile station forthe period informed in the absence message. Such a system causes a highamount of signalling and is therefore suitable for small systems only.

All additional facilities according to the invention required of theradio network may be implemented in a call control computer of theexchange MX, which computer controls call set-up and signalling (e.g.messages) anyway. The previously mentioned data set as well as thetimers measuring the sleeping time may be implemented in the memory ofthe call control computer.

Instead of for battery saving (sleeping), the MS may utilize the timeduring which it is unreachable for the system also for other measures,which it cannot take during monitoring of the control channel. Forinstance, the MS may make measurements on adjacent control channels/basestations in order to search for the best base station and have itavailable, if it is necessary to change the control channel, when thesignal of the present base station becomes weaker with the moving MS.The MS may also utilize the absence time for visiting another radiosystem or for a direct communication with another MS without a system.The first or home radio network does not need to know what the MS isdoing during the absence, the only essential information for thatnetwork being that the MS cannot be reached during this period. Theprocessor unit 25 of the MS may automatically select, if necessary, theoperation which shall be performed during each "sleeping period".

The figures and the description associated with them are only intendedto illustrate the present invention. As to the details, the radio systemaccording to the invention may vary within the scope and spirit of theattached claims.

We claim:
 1. A radio system, comprising:a radio network having aplurality of base stations; a plurality of mobile radio stations eachhaving a user interface allowing a user to select between a normaloperating mode and an alternative operating mode for the respectivemobile radio station; each said mobile radio station in said normaloperating mode thereof, in case of no ongoing call, being arranged tocontinuously monitor a control channel of a one of said base stations towhich said mobile radio station is currently registered, said one basestation thereby then being a serving base station for said mobile radiostation; each said mobile radio station being responsive to selection ofsaid alternative operating mode by the user, for stopping monitoring ofsaid control channel of said serving base station for absence periodsdecided by said mobile radio station and for monitoring said controlchannel between said absence periods, and for informing said radionetwork of beginning and duration of each said absence period by meansof an absence message prior to each absence period; said radio networkbeing responsive to receiving each said absence message for ceasingsending of messages to said mobile radio station on said control channelof said serving base station during each absence period indicated byeach absence message.
 2. A radio system, comprising:a radio networkhaving a plurality of base stations; a plurality of mobile radiostations each having a user interface allowing a user to select betweena normal operating mode and an alternative operating mode, for therespective mobile radio station, episodes of operating in saidalternative operating mode equating to respective absence periods; eachsaid mobile radio station in said normal operating mode thereof, in caseof no ongoing call, being arranged to continuously monitor a controlchannel of a one of said base stations to which said mobile radiostation is currently registered, said one base station thereby being aserving base station for said mobile radio station; each said mobileradio station being responsive to selection of said alternativeoperating mode by the user, for informing said radio network ofselection of said alternative operating mode; said radio network beingresponsive to selection of said alternative operating mode for saidmobile radio station, for commanding said mobile radio station, bycommands, to stop monitoring said control channel of said serving basestation for said absence periods; said mobile radio station beingresponsive to said commands from said radio network for stoppingmonitoring said control channel of said serving base station for saidabsence periods and for monitoring said control channel betweentemporally succeeding ones of said absence periods; said radio networkbeing arranged to cease sending of messages to said mobile radio stationon said control channel of said serving base station during said absenceperiods.
 3. A radio system according to claim 1 or 2, wherein:saidmobile radio station is arranged to measure adjacent base stationsduring at least some of said absence periods.
 4. A system according toclaim 1 or 2, wherein:said mobile radio station is in a power-savingmode during each said absence period.
 5. A system according to claim 1or 2, wherein:said mobile radio station is arranged to be in a directradio communication with another mobile radio station or to communicatewith another radio system during the absence period.
 6. A systemaccording to claim 1 or 2, wherein:said mobile radio station comprises acontrol processor controlling operation of said mobile radio station, atransceiver, a synthesizer, an audio unit to process audio signals to besent and received and wherein all operations of said mobile radiostation are continuously switched on in said normal operating mode, andwherein said alternative operating mode is a power-saving mode, in whichsaid control processor is arranged to control at least said transceiver,said synthesizer and said audio unit to be switched on and off for saidabsence periods.
 7. A system according to claim 6, wherein:saidprocessor means is also switched off for each said absence period; andsaid mobile radio station comprises a timer for switching on saidprocessor means after each said absence period.
 8. A system according toclaim 6, wherein:said processor means operates during each absenceperiod at a lower clock frequency than in said normal operating mode. 9.A system according to claim 1 or 2, wherein:each said absence period isat least 1 second in duration.
 10. A system according to claim 1 or 2,wherein:each said absence period is at least 10 seconds in duration. 11.A system according to claim 1 or 2, wherein: each said absence period isat least 20 seconds in duration.
 12. A system as claimed in claim 1 or2, wherein:each said absence period is between 1 and 20 seconds induration.
 13. A mobile radio station for a radio system including aradio network having a plurality of base stations including a servingbase station serving said mobile radio station to which said mobileradio station is registered at a given time, said mobile radio stationcomprising:a user interface allowing a user to select between a normaloperating mode and an alternative operating mode for said mobile radiostation; and said mobile radio station in said normal operating modethereof, in case of no ongoing call, being arranged to continuouslymonitor a control channel of said serving base station; said mobileradio station being responsive to selection of said alternativeoperating mode by the user, for stopping monitoring said control channelof said serving base station for absence periods decided by said mobileradio station and for monitoring said control channel between saidabsence periods, and for informing said radio network of the absence anda duration of each said absence period by means of an absence messageprior to each said absence period, so as to enable said radio network tocease sending of messages to said mobile radio station on said controlchannel of said serving base station during the respective said absenceperiod indicated by the respective said absence message.
 14. A mobileradio station for a radio system including a radio network having aplurality of base stations including a serving base station serving saidmobile radio station to which said mobile radio station is registered ata given time, said mobile radio station comprising:a user interfaceallowing a user to select between a normal operating mode and analternative operating mode for said mobile radio station; said mobileradio station in said normal operating mode thereof, in case of noongoing call, being arranged to continuously monitor a control channelof serving base station; said mobile radio station being responsive toselection of said alternative operating mode by the user, for informingsaid radio network of the selection of said alternative operating mode,so as to authorize said radio network to command said mobile radiostation, using commands, to stop monitoring said control channel of saidserving base station for absence periods and to cease sending ofmessages to said mobile radio station on said control channel of saidserving base station during said absence period; and said mobile radiostation in said alternative operating mode being responsive to saidcommands from said radio network for stopping monitoring said controlchannel of said serving base station for said absence periods and formonitoring said control channel between said absence periods.